This invention relates to a cable box. In particular, it relates to a junction box for electrical non-metallic sheathed cable, the box being an individual unit or part of an assembly to mount a light fixture.
Conventional cable boxes have knockouts in the walls of the box so that cable can pass into the cavity of the box for junction or other purposes. So as not to disturb the junction or the cables in the box, for instance, when the cables are moved outside of the box, it is desirable to have a clamping means to secure the cable in a relatively stable manner to the box. One kind of cable where such clamping is particularly desirable is that cable commercially known as "Romex", which is a multiconductor cable.
Many forms of clamping means are known but in the applicant's experience they suffer from one or another disadvantage. In one known junction box, clamping plates are operable against the wall adjacent the apertures through which the cable passes into the box. The corners of this box are bevelled such that effectively the clamp operates against a surface at 45.degree. to each of the adjacent sides of the box. In order to have this clamp work effectively, a substantial portion of the box is removed by these bevelled walls thereby substantially reducing the effective working volume in the box. The clamp is operated by a screw means activated internally, and because the shank of the screw is open to the inside of the box, the danger exists that the tool for turning the screw, and the turning shank itself, can damage the cable within the box. The bevelled effect permits screws to be directed to the open face of the box, thereby facilitating turning the screw. In other cases the screw head is angularly offset relative to the opening, thereby creating difficulties in operation.
It is known to provide detents in the clamping plate and the wall against which the clamping plate moves, so that the cable is pinched into security with the wall. A disadvantage of this is that the cable could be weakened in the efforts made in securely anchoring the cable to the box. Another reason for the bevelled face in this prior art device is that as the screw passes outside of the box during wedging, it will not protrude beyond the back wall of the box.
Another prior art device comprises a rectangular junction box in which apertures are provided in the metal side walls of the box enabling cables to pass into the box. A clamping device is operable from inside the box and includes a screw which passes through the back wall of the box so that the clamping plate is forced downwardly onto the back plate of the cable box. As the screw is tightened it progressively protrudes further beyond the back of the box. This protrusion is dangerous in cases where the box is not mounted within a wall, and, when mounted within a wall, it is a problem where there is a restricted space behind the surface of the wall. This prior art device requires covering legs which move across the apertures in the side walls as the clamping means is drawn against the back wall thereby to cover these apertures from the dangerous ingress of tools and the like into the junction box. Accordingly, more material is needed in this clamping device than is actually required to effect clamping.
In yet another form of the prior art, a threaded tube and nut formation is applied for fitting about a knocked-out aperture in a wall of a cable box. Extending from the threaded tube through which the cable passes is a saddle for receiving cable and which cooperates with a movable arm which may be moved by means of two spaced screws either towards or away from the saddle. A disadvantage of such clamping mechanism is that it must be spaced from the adjacent walls of the box to permit installation and hence the cable entering the cable box must necessarily pass into the center of the box thereby wasting space in the box. The material required for such a clamping mechanism is also a relatively heavy gauge, and installation of the clamping means requires several operations making its use unduly expensive.
There is accordingly a need to provide a cable box which permits the maximum use to be made of the inside housing of the box, while at the same time providing a clamping mechanism strategically located to effect clamping. The necessary clamping mechanism should avoid the risk of damage to the cable being clamped, and at the same time the clamping mechanism should not require insertion of tools or the like into the box. It is also desirable to minimize the number of portions and sharp edges of the clamping mechanism exposed in the box thereby minimizing the danger of damage to the box contents. Furthermore, the clamping mechanism should be easily operable without access to the interior of the box.